The referenced U.S. Pat. No. 4,370,927, FISCHER, describes a threading apparatus for a rotary printing machine to thread webs therein. The structure includes a tubular guide, within which a threading element, fitting within the tubular guide, can be pulled. The tubular guide is formed with a longitudinal slit through which a holder bracket for paper webs to be threaded into the machine can extend. Preferably, and as disclosed, the tubular guide has circular cross section. Threading apparatus of this kind enables paper webs or other webs in which printing is to be done to be threaded in a rotary printing machine and, further, to guide the web accessory or auxiliary apparatus, for example about turning rods, guide rollers, and the like. If the web is to be guided about turning rods and the like, it is necessary that the web not only must be looped about the rod but, if the guide rods are located at an angle with respect to the longitudinal extent of the web, the threading element must, additionally, be twisted so that the longitudinal slit will follow the path of the web. Otherwise, the web will not follow an angular path as determined by a guide rod or guide roller which is positioned at an angle with respect to the web.
In the past, guide rod sections which required a spiral slit therein were made specially by a process similar to cutting a long spiral slit into a rod, that is, by a process similar to forming a spiral thread. A longitudinal as well as rotary movement was impressed on a guide section, resulting in a hollow segment of the guide rod in which the slit extended in a spiral direction, similar to the path of a flank of a thread, which could guide a pull element about an angularly positioned turning rod, guide roller or the like.
As can readily be seen, manufacturing such guide elements specially on a machine which provides for conjoint rotary as well as longitudinal feed of a cutting element is expensive. Additionally, if at the same time the guide element is to be bent further operating or working steps are necessary.